Servocontrol for dual hydraulic systems

ABSTRACT

An improved servocontrol for redundant hydraulic fluid systems employing dual pressure sources each operating a separate actuator simultaneously to perform a common function. Two servo valve devices are employed, with each including valve elements connected in both hydraulic systems, thereby providing parallel control circuits from each pressure source to its associated actuator. The two servo valve devices are operated in synchronism by an input assembly permitting independent operation of one servo valve device in the event of jamming of the other. The parallel circuits, controlled through separate, independently operably valves, eliminate the possibility of a hydraulic lock in one actuator preventing operation of the other.

0 llmted States Patent [151 3,640,185

Korsak 1 Feb. 8, 1972 [54] SERVOCONTROL FOR DUAL 3,527,143 9/1970 Hayter..9l/4l 1 HYDRAULIC SYSTEMS Primary Examiner-Edgar W. Geoghegan [72]Inventor: Kazunierz Korsak, Newtovvn, Pa. A"0mey Beveridge & De Grandi73 A ne Piasecki Aircraft Cor oration Phil d l- 1 mg 8 phi, Pa p a e [57ABSTRACT [22] Filed: Jan. 7, 1970 An improved servocontrol for redundanthydraulic fluid systems employing dual pressure sources each operating a[2]] Appl. No.1 1,151 separate actuator simultaneously to perform acommon function.'Two servo valve devices are employed, with each includ-[52] U S Cl 91/411 R 91,411 A 91/413 ing valve elements connected inboth hydraulic systems, [5 Flsb 11/16 thereby providing parallel controlcircuits from each piessure [58] Fie'ld 41 l A 413 source to itsassociated actuator. The two servo valve devices are operated insynchronism by an input assembly permitting independent operation of oneservo valve device in the event [56] References cued of jamming of theother, The parallel circuits, controlled UNITED STATES PATENTSthroughseparate, independently operably valves, eliminate 2 597 4185,1952 w tb t 1 91/216 A X 7 the possibility of a hydraulic lock in oneactuator preventing GS ury e a o ti f h (hen 2,597,419 5/1952 Westburyet al. ...9l/2l 6 A X p 3,272,062 9/1966 Flippo et al. ..9l/4l 1 A X 12Claims, 5 Drawing Figures SlERVOCONTROL FOR DUAL IIYDRAULIC SYSTEMS Thisinvention relates to redundant hydraulic control systems, and moreparticularly to an improved fail-safe mechanically actuated controlvalve mechanism for parallel, redundant hydraulic actuator controlsystems especially useful in aircraft.

In hydraulic actuator systems where a high degree of operationalreliability is essential, such as in servocontrol systems for aircraft,it is the conventional practice to provide redundant hydraulic systemswhich operate simultaneously to act upon a common output element toproduce the desired aircraft control surface movement. The redundantsystems are provided solely for the purpose of improving reliability inthat, in the event of failure of one hydraulic system, the actuator maystill be operated, without interruption, by the other system. Thelikelihood of simultaneous failure of both systems is, of course, muchmore remote.

Even in such critical applications as in the control of operation of theprimary flight control surfaces of an aircraft, the prior art dualhydraulic control systems have, until recently, been generallyconsidered satisfactory if the output element is connected to andoperated by two separate pistons each driven by fluid directed from itsrespective fluid system by separate servocontrol valves. The pistons, orspools, of'the two servo valves of these prior art systems wereconventionally rigidly connected to each other to assure synchronizationof operation of the two actuator pistons. However, this arrangementcreated the possibility that jamming of the spool in one servo valvewould render the entire system inoperative due to the two valve spoolsbeing rigidly connected. In an effort to avoid this contingency, systemshave been provided which employ separate, independent servo valves, onefor each of the respective actuator pistons, with electrical controlsand/or mechanical linkage mechanisms being employed to synchronizemovement of the servo valves. Such systems have not, however, beenentirely satisfactory due primarily to the unreliability of known valvelinkages and control mechanisms.

The above-mentioned disadvantages of the prior art are overcome, and amuch higher degree of reliability is provided, by the present inventionin which means are provided for assuring synchronized movement ofseparate servo valve spools and, at the same time, assuring freedom ofmovement of one servo valve spool in the event of jamming or freezing ofthe other. Further, the present invention provides means for avoidingthe possibility of hydraulic lockin the main actuator powerjunit in theevent of one of the servo valve spools becoming jammed in the neutralposition of the valve. This is accomplished by employing the essentialelements of two conventional servocontrol valves, with the two servovalve spools being independently connected to an input element so thatmovement in the mechanical control input to operate the two servo valvesnormally will not result in any relative motion between the valvespools. However, should one valve spool become jammed, the independentconnection of the valve spools permits the second spool to be moved bythe input element independently of the jammed spool.

The two servo valves are constructed to simultaneously serve twoindependent hydraulic systems, and are each con nected in the twosystems to provide parallel control circuits for each actuator piston.Thus, pressure and return lines branch off from each of the two separatehydraulic systems to each of the two servo valves, and lines from eachside of each of the actuator pistons run to both of the servo valves sothat, in the event that one valve spool becomes jammed in a neutralposition, a hydraulic lock is avoided by the lines from the other valverunning to both of the actuator pistons.

A primary object of the present invention is to provide an improvedhydraulic actuator control means.

Another object of the present invention is to provide an improved meansfor synchronizing movement of parallel connected servo valves.

Another object of the present invention is to provide a failsafe meansfor controlling a hydraulic actuator employing a plurality of parallelconnected servo valves.

Other objects and advantages of the present invention will becomeapparent from the following detailed description, taken with referenceto the accompanying drawings, in which:

FIG. I is'a schematic view, in section, of a hydraulic actuatorcontrolaccording to the present invention;

FIG. 2 is an elevation view, partially in section, of the servo valvemechanism schematically illustrated in FIG. 1;

FIG. 3 is a fragmentary sectional view of the input element of theservomechanism shown in FIG. 2;

FIG. 4' is a schematicview of an alternate embodiment of the invention;and

FIG. 5 is an elevation view, partially in section, of the embodiment ofthe invention schematically illustrated in FIG. 4.

Referring now to the drawings in detail, a servocontrol actuator systemaccording to the present inventionis indicated generally by thereference numeral 10 and includes a main cylinder body 12 having a pairof axially aligned, spaced cylinders l4, 16 formed. therein. A firstpiston 18 is mounted in cylinder 14 for axial, reciprocating movementtherein, and a second piston 20 is mounted in cylinder 16 for axial,reciprocating movement therein. A common piston rod 22 extends throughcylinder body 12 and is rigidly attached to pistons 18 and 20 formovement therewith and to prohibit relative axial movement between thetwo pistons. Piston rod 22 projects axially from one end of the cylinderbody I2 to form an output element 23 which may be attached, as by pin 24and bracket 26 to a rigid member such as the frame structure of anaircraft, indicated generally by the reference numeral 28. The oppositeend of the cylinder body 12 is provided with a rigid, outwardlyprojecting connector element 30 having an opening 32 formed therein forpivotal connection, through suitable linkage not shown, to a movablecontrol sur face of an aircraft. Alternatively, connector 30 may beconnected to the rigid structure 28 and the outputmember 23 connected tothe movable control surface.

A servocontrol valve mechanism, indicated generally by the referencenumeral 34, is provided to direct hydraulic fluid under pressure(pressure fluid) from a source 8-1 to cylinder 16, at either side ofpiston 20, selectively. Similarly, servo valve 34 directs pressurizedfluid from a'second source 5-2 to cylinder 14, at either side of piston18, selectively. As best seen in FIG. 1, servo valve mechanism 34includes a valve body 36 having slidably mounted therein a first valvespool 38 and a second valve spool 40. Spools 38 and 40 are mountedcoaxially within a common bore 42 in valve body 36.

Pressure fluid from source S-l enters the valve body 36 through inlet 44and passes through conduit 46 into the chamber 48 defined by the lands50 and 52 on spool 38, and the inner wall of bore 42. Movement of spool38 to the left in the direction of arrow 54 in FIG. 1 will permit thepressure fluid to flow from chamber 48 through conduit 56 into chamber58 of cylinder 16, thereby tending to force piston 20 to the rightrelative to valve body 12. Actually, since the piston rod 22 and outputmember 23 are connected to a rigid frame member 28, the application offluid pressure in chamber 58 will move the actuator cylinder body 12 andthe valve body 36 to the left until the input signal, resulting frommoving valve spool to the left, is cancelled. This movement will resultin fluid in chamber 60 of cylinder 16 being forced out through conduit62 into the chamber 64 defined by lands 52 and 66, then out throughconduit 68 and outlet 70 to return to the source 8-].

Simultaneously, pressure fluid from the source S2 will be directed intovalve body 36 through inlet 72 and pass through conduit 74 to thechamber 76 defined by lands 78 and 80. From chamber 76, the pressurefluid will pass through conduits 82, 83 into the chamber 84 of cylinder14 to urge piston 18 in the same direction that piston 20 is being urgedby the pressure fluid from source 8-1. At the same time, any fluid fromchamber 86 of cylinder I4 will be urged through conduits 88, 89 into thechamber 90 defined by lands and 92 on valve spool 38. From the chamber90, the fluid can return through conduit 92 and outlet 94 to be returnedto source S-2.

Thus, it is seen that movement of valve spool 38 to the left, in thedirection of arrow 54 will direct pressure fluid from source S1 tochamber 58 of cylinder 16, and simultaneously will direct pressure fluidfrom source S2 to chamber 84 of cylinder 14. Thus, the pressure fluid incylinders 14 and 16 simultaneously urge the cylinder body 12 to the leftin the direction of movement of valve spool 38.

in the event of movement of the valve spool 38 to the right, in thedirection of arrow 96, pressure fluid from source S-l will flow fromchamber 48 through conduit 62 into chamber 60 of cylinder 16, and fluidin the chamber 58 will be urged out through conduit 56 into the chamber98 defined by lands 50 and 100, then out through conduits 102 and 68 tobe returned to source S-l. Similarly, pressure fluid from source -2 willflow from chamber 76 through conduits 89 and 88 into chamber 86, andfluid from chamber 84 will be urged out through conduits 83 and 82 intothe chamber 104 defined by lands 78 and 106, then out through conduits108 and 92 to be returned to source S-2.

Valve spool 40 is coupled to spool 38 for simultaneous movementtherewith through a resilient input coupling assembly 110, describedmore fully herein below. As seen in FlG. 1, valve spool 40 is providedwith a series of spaced lands corresponding substantially with the landson valve spool 38, and forms, in combination with the inner wall of bore42, a second servo valve connected in parallel with the servo valvedefined by spool 38 to provide parallel controlled paths for pressurefluid from source S-l to cylinder 16 and from source S-2 to cylinder 14.Referring specifically to FIG. 1, it is seen that conduit 112 isconnected in fluid communication with conduit 46 to direct pressurefluid from source S-1 into the fluid chamber 114 defined by lands 116and 118. In the event of movement of spool 40 to the left, in thedirection of arrow 54, the pressure fluid will be directed throughconduit 120 to the conduit 56, thereby providing an alternate,controlled path for the pressure fluid from source S-l to the chamber58. At the same time, pressure fluid from source S-2 will be directedthrough conduit 122, connected in fluid communication with conduit 74,into the chamber 124 defined by lands 126 and 128. From the chamber 124,this pressure fluid will flow through conduits 130 and 83 to the chamber84. The resultant relative movement of piston will urge fluid out ofchamber 60 into conduit 132, connected in fluid communication withconduit 62, and into the chamber 134 defined by lands 118 and 136. Fromchamber 134, this fluid will flow out through conduit 138, connected influid communication with conduit 68, and be returned to the source S-l.Similarly, movement of piston 18 relative to cylinder 14 will urge fluidfrom chamber 86 out through conduit 140, connected in fluidcommunication with conduit 88, and into the chamber 142 defined by thelands 128 and 144. From chamber 142, this fluid will flow throughconduit 146 into conduit 92 and be returned to source 5-2.

In the event of movement of spool 40 to the right in the direction ofarrow 96, fluid under pressure from source Sl will flow from chamber 114through conduits 132 and 62 into the chamber 60, and fluid from chamber58 will flow out through conduits 56 and 120 into the chamber 148defined by lands 116 and 150. Fluid from this chamber 148 will then flowout through conduit 152 into conduit 138 and be returned to the sourceS-l in the manner described above. Similarly, fluid from chamber 124will be directed through conduits 140 and 88 into chamber 86, and fluidfrom chamber 84 will flow through conduits 83 and 130 into the chamber154 defined by lands 126 and 156. Fluid from chamber 154 will then flowout through conduit 158 into conduit 146 and be returned to source S-2through conduit 92 in the manner described above.

To avoid the possibility of any mixing of fluids from sources S1 andS-2, by leakage along the valve spools 38 and 40, a suitable drain orvent 160 is provided between lands 66 and 106, and a similar vent 164 isprovided between lands 136 and 156. Also, a vent 162 is provided betweenlands 92 and 150,

and a suitable vent 166 is provided along piston rod 22 between chambers60 and 84.

Referring now particularly to FIG. 2 and 3, it is seen that valve spool38 is provided with an axial bore 168 extending therethrough, and spool40 has an elongated cylindrical stem 170 integrally formed on its endadjacent spool 38. Stem 170 is disposed in and extends through bore 168.The stem 170 and the end of spool 38 project outwardly from body 36 andextend into an opening 172 in the bottom of a cup-shaped housing 174 ofresilient input member 110. The stem 170 is freely slidable within thebore 168, but the respective elements are spring loaded and resilientlyretained into fixed relative positions within the cup 174.

Referring to FIG. 3, it is seen that spool 38 terminates in an outwardlydirected flange 176, and a rigid annular collar 178 extending around thebody of spool 38 is urged into firm engagement with the flange 176 by acoil spring 180 disposed between the end wall 182 of cup 174 and thecollar 178. Movement of the collar 178 away from the end wall 182 islimited by an inwardly directed shoulder 184 formed on a sleeve 186snugly received within the cup 174 and having its end bearing againstwall 182. Sleeve 186 is retained in fixed position within the cup 174 bya cylindrical sleeve 188 and a pair of sleeves 190, 192, having inwardlydirected shoulders 194, 196, respectively, formed thereon. A cap member198 is threadably attached to the open end of cup member 174 and rigidlyclamps the sleeve members 186, 188, 190 and 192 against the end wall182.

To prevent any possible fluid leakage through bore 168 along stem 170,an O-ring seal 200 is positioned within a recess 202 in the end of spool38. The seal is retained in place by a sleeve 204 having an outwardlydirected flange 206 overlying flange 176. The combined thicknesses offlanges 176 and 206 equals the thickness of flange 184.

A second annular collar 208 is disposed around the end of stem 170,within the cylindrical sleeve 188, and is urged into engagement with theflange 184 and the flange 206 by a resilient coil spring 210 disposedbetween the collar and the flange 194. Springs 180 and 210 are eachcompressed against flange 184 to provide a preload, in either axialdirection, for the spool 38, which preload must be overcome before anyrelative movement between the housing 17 4 and spool 38 may be realized.

The stem 170 terminates in a reduced diameter, threaded portion 212projecting through the bore 168. The juncture of threaded portion 212with the body stem 170 defines a shoulder 214 for supporting a flatwasher 216 which is rigidly retained on the threaded portion 212 by alocknut 218. An annular collar 220 disposed within the sleeve 190 isurged in the direction of washer 216 and shoulder 196 by a coil spring222 disposed between the collar and flange 194. Another annual collar224 is disposed within annual sleeve 192 and is resiliently urged in thedirection of washer 216 and flange 196 by a resilient coil spring 226between the flange 196 and the end wall 228 on threaded cap 198. Washer216 is the same thickness as the flange 196, and springs 222 and 226 arecompressed to resiliently urge collars 220 and 224 toward one another toclamp the flange 196 and washer 216 therebetween. Thus, the preload inthe coil springs resiliently retain the end of the stem 170 in fixedrelation within the housing 174. A coupling member 230 is rigidly fixedon the end of threaded cap 198, and has an opening 232 formed thereinfor pivotally connecting the assembly to a suitable input linkage, nowshown.

From the above, it can be seen that the spools 38 and 40 are springloaded in fixed relation to one another for simultaneous movement uponany movement of the input member 110. However, in the event of one ofthe spools becoming jammed, a slight increase in input force willovercome the preload in the spring involved, so that the other spool maybe actuated independently of the jammed spool.

By providing two separate servo valve devices, each connected in bothconduit systems, parallel control paths are provided from each pressuresource to its associated actuator cylinder. Since these parallel pathsare controlled by two different servo valve devices which are normallyoperated simultaneously but operably independently, a very high degreeof reliability is achieved. If one valve spool were to become jammed inthe closed, or dead center position (the position illustrated in FIGS. 1and 4), the other spool would still be operable to provide a controlledpath for fluid to each of the actuator cylinders, thereby avoiding anypossibility of a hydraulic. lock in one system preventing operation ofthe other. This would be true regardless of which servo valve spoolbecamejammed.

Referring now to FIGS. 4 and 5 of the drawings, an alternate embodimentof the invention will be described. In this alternate embodiment, theservo valve spools are positioned in separate bores in the valve body,and are coupled together through a mechanical linkage for simultaneousmovement. The mechanical linkage, however, provides for independentmovement of the respective valve spools in the event of jamming onespool, thereby avoiding the possibility of a hydraulic lock in the samemanner as the spring loaded input assembly 110 illustrated in FIGS. 1-3.

The actuator assembly of this alternate embodiment is indicatedgenerally by the reference numeral 300 and includes a cylinder body 312having a pair of axially aligned cylinders 314, 316 formed therein. Afirst piston 318 is mounted in cylinder 314 for axial reciprocatingmovement therein, and a second piston 320 is similarly mounted incylinder 316. A common piston rod 322 extends through cylinder body 312and is rigidly attached to pistons 318 and 320 for movement therewithand to prohibit relative axial movement between the two pistons. Pistonrod 322 extends axially from one end of the cylinder body to form anoutput element 323 which may be attached, in the manner described above,to a rigid member such as frame structure of an aircraft, now shown. Theopposite end of cylinder body 312 is provided with a rigid, outwardlyprojecting connector element 330 having an opening 332 formed thereinfor pivotal connection, through suitable linkage, to a moveable controlsurface of the aircraft.

The servocontrol valve mechanism of this embodiment, indicated generallyby the reference number 334, is operable to direct pressure fluid from asource S-l, selectively to either side of the piston 320 in cylinder316, and simultaneously to direct pressure fluid from source S-2selectively to either side of piston 318 in cylinder 314. As indicatedschematically in FIG. 4, the servo valve mechanism 334 includes a valvebody 336 having a first valve spool 338 slidably mounted within a bore339, and a second valve spool 340 slidably mounted within a second bore342.

Pressure fluid from source S-1 enters the valve body 336 through aninlet 344 and passes through conduit 346 into chamber 348 defined by thelands 350 and 352 on valve spool 338. Movement of the valve spool 338 tothe left in the direction of arrow 354 in FIG. 4 will permit thepressurefluid to flow from chamber 348 through conduit 356 into thechamber 358 of cylinder 316. Since piston is fixed, the pressure inchamber 358 will tend to force cylinder body 312 to the left in thedirection of the movement of valve spool 338. At the same time, fluid inchamber 360 of cylinder 316 will be forced out through conduit 362 intothe chamber 364 defined by lands 352 and 366, then out through conduits368, 369, 370 and outlet 371 to be returned to source S-1.

Simultaneously, pressure fluid from the source 8-2 will be directed intothe valve body 336 through inlet 372 and pass through the conduit 374into the chamber 376 defined by the lands 378 and 380. From the chamber376, the pressure fluid will pass through conduit 382 into the chamber384 of cylinder 14 to urge the cylinder body 312 to the left. At thesame time, fluid in chamber 386 of cylinder 314 will be urged throughconduit 388 into the chamber 390 defined by the lands 380 and 392 onvalve stem 338. From the chamber 390, the fluid may return, throughconduits 392, 393 and outlet 394 to source S-2. Thus, as in the firstembodiment, movement of valve spool 338 to the left, in the direction ofarrow 354, will direct pressurized fluid from the source S-1 to chamber358 and simultaneously will direct pressure fluid from source 8-2 tochamber 384 so that pistons 318 and 320 cooperate to urge the piston rod322 to the right relative to the cylinder body 312.

In the event of movement of the valve spool 338m the right, in thedirection of arrow 396, pressure fluid from the source S-l will flowthrough the chamber 348 and conduit 362 into chamber 360 of cylinder316, and fluid in .the chamber 358 will be urged out through conduit 356to the chamber 398 defined by lands 350 and 400, then out throughconduit 370 to be returned to source S1. Similarly, pressure fluid fromsource S-2 will flow from chamber 376 through conduit 388 into chamber386, and fluid from chamber 384 will be urged out through conduit 382into the chamber 404 defined by the lands 378 and 406, then throughconduits 408, 392, and 393 to be returned to source S-2.

Valve spool 340 is coupled to valve spool 338 for simultaneous movementtherewith through a whiffeltree type linkage comprising a transversebeam 409 having one end pivotally connected to the projecting end ofvalve spool 338, as by a pin 410, and having its other end pivotallyconnected, in a similar manner, to valve spool 340 by a pin 411. Aninput linkage 412 is pivotally connected, as by pin 413, to the centerof beam 409 so that any force applied through the input linkage 412 willbe equally distributed between valve spools 338 and 340. The pivotaljoints formed by pins 410 and 411 are provided with sufficient clearanceto permit limitedmovement of the valve spools with respect to oneanother, so that, in the event of one spool becoming jammed, the othermay still be actuated by a force applied through the input linkage 412.In FIG. 5, an alternative means of providing for this relative movementis illustrated in which an intermediate link 414 is pivotally connectedbetween the beam 409 and the end of valve 340.

It is believed apparent that, if desired, the input linkage 412 could berigidly connected to beam 409, and the spools 338 and 340 in turnconnected to the ends of the beam by a preloaded spring coupling in amanner similar to that employed in the embodiment illustrated in FIGS.1-3.

The valve spool 340 is provided with a series of spaced landscorresponding substantially with the lands on valve spool 338 to form asecond servo valve connected in parallel with the servo valve defined bythe valve spool 338 to supply pressure fluid from source 8-1 to cylinder316 and from source 8-2 to the cylinder 314. Referring specifically tothe schematic illustration in FIG. 4, it is seen that conduit 346directs pressure fluid from the source S1 into the fluid chamber 415defined by lands 416 and 418. This pressure fluid will then flow throughconduit 420 into conduit 356, thereby providing an alternate path forthe pressure fluid from the source S-l to the chamber 358. At the sametime, pressure fluid from source 8-2 will be directed through theconduit 374 into valve chamber 424 defined by lands 426 and 428. Fromthe chamber 424, this pressure fluid will flow through conduits 430 and382 to the chamber 384.

Relative movement of the piston 320 to the right in cylinder 316 willurge fluid out of chamber 360 into the conduit 432, connected in fluidcommunication with conduit 362, and into the chamber 434 defined bylands 418 and 436. From chamber 434, this fluid will then flow outthrough conduits 368, 369, and 370 to be returned to the source S1.Simultaneously, relative movement of piston 318 to the right in cylinder314 will urge fluid out of chamber 386 through conduit 440 connected influid communication with conduit 388, into the chamber 442 defined bythe lands 428 and 444. From chamber 442, this fluid will flow throughconduits 392 and 393 to be returned to the source 5-2.

In the event of movement of the input linkage 412 to the right, in thedirection of arrow 396, fluid under pressure from source S-l will flo wfrom the chamber 415 through conduits 432 and 362 into the chamber 360,and fluid from the chamber 358 will flow out through conduits 356 and420 into the chamber 448 defined by lands 416 and 450. Fluid from thischamber 448 will then flow out through conduits 370 and be returned tosource S-l. Similarly, fluid from the chamber 424 will be directedthrough conduits 440 and 388 into chamber 386, and the fluid chamber 384will flow out through conduits 383 and 430 into the chamber 454 definedby lands 426 and 456. Fluid from chamber 454 will then flow throughconduits 458, 392 and 393 to be returned to the source S-2.

A suitable O-ring seal 460 is provided between lands 366 and 406 onvalve spool 33S, and a similar O-ring 462 is provided between lands 436and 456 on valve spool 340. Alternatively, as illustrated in FIG. 5, asuitable drain, or vent, 466 may be provided between chambers 364 and404, and a similar drain 468 may be provided between chambers 434 and454. A suitable drain 470 is also provided along piston rod 322 betweenchamber 360 and 384, as illustrated in FIG. 4.

From the above, it should be apparent that either illustrated embodimentof the invention will provide a highly reliable, hydraulically redundantactuator control system which clearly avoids the above-describeddeficiencies of the prior art devices. By providing parallel paths forthe pressure fluid from the first source, through the two servo valvedevices, to operate one actuator piston and simultaneously providingparallel control paths for the pressure fluid from the second sourcethrough the same two servo valve devices, to operate the second actuatorpiston, both pistons will be operated in their normal manner even if oneof the servo valve spools is jammed closed. Yet, by maintaining the twofluid systems entirely separated, failure of one system, as by loss offluid pressure, will not in any way interfere with operation of thedevice through the other system.

While the actuator has been described as a linear reciprocating fluidmotor, or cylinder and piston device, it should be apparent that theservo control assembly would be equally operable with various devices.For example, the servocontrol could readily be employed with a rotaryhydraulic actuator of the general type illustrated in the US. Pat. No.3,318,20l. Thus, while I have disclosed and described preferredembodiments of my invention, 1 wish it understood that i do not intendto be restricted solely thereto, but I do intend to include allembodiments thereof, which would be apparent to one skilled in the artand which come within the spirit and scope of my invention.

lclaim:

l. A hydraulic actuator system comprising, in combination, first andsecond fluid chambers, a piston mounted in each of said fluid chambers,means connecting said pistons for equal, simultaneous movement withintheir respective fluid chambers, a first source of pressure fluid, firstconduit means connecting said first source to said first fluid chamber,a second source of pressure fluid, second conduit means connecting saidsecond source to said second fluid chamber, a servo valve assemblyoperatively connected in said first conduit means and providingcontrolled parallel fluid circuits between said first source and saidfirst fluid chamber, said servo valve assembly also being operativelyconnected in said second conduit means and providing controlled parallelfluid circuits between said second source and second fluid chamber, andsignal input means operating said servo valve assembly to control theflow of pressurized fluid through each of said fluid circuitssimultaneously.

2. The hydraulic actuator system defined in claim 1 wherein said servovalve assembly comprises first and second servo valves each operativelyconnected in said first conduit means and in said second conduit means,said first and said second servo valves cooperating to provide saidparallel circuits between said first source and said first fluid chamberand between said second source and said second fluid chamber.

3. The hydraulic actuator system defined in claim 2 wherein said signalinput means comprises an input assembly normally applying equaloperating loads to said first and said second servo valves to therebysynchronize operation of the two valves.

4. The hydraulic actuator system defined in claim 3 wherein said signalinput means further comprises means for operating one of said servovalves independently of operation of the other of said servo valves inthe event said other servo valve becomes inoperable.

5. The hydraulic actuator system as defined in claim 4 wherein saidfirst and said second servo valves are positioned in side-bysiderelation, and said signal input means comprises a whiffletreeoperatively connected to each of said servo valves for operationthereof.

6. The hydraulic actuator system as defined in claim 4 wherein saidsignal input means further comprises a prestressed resilient connectorassembly connected to each of said servo valves, said connector assemblybeing deformable by either of said servo valves only upon said valvesencounter ing a substantial increase in resistance to operation.

7. A hydraulic actuator system comprising, in combination, first andsecond fluid chambers, a pair of pistons mounted one in each of saidfluid chambers, an output member, means connecting said pistons to saidoutput member for simultaneous movement therewith, a first source ofpressure fluid, first conduit means connecting said first source to saidfirst fluid chamber, a second source of pressure fluid, second conduitmeans connecting said second source to said second fluid chamber, firstservo valve means connected in said first eonduit means and providing acontrolled circuit for pressure fluid between said first source and saidfirst fluid chamber and connected in said second conduit means andproviding a controlled circuit for pressure fluid between said secondsource and said second fluid chamber, second servo valve means connectedin said first conduit means in parallel with said first servo valve andproviding a second controlled circuit for pressure fluid between saidfirst source and said first fluid chamber and in said conduit means inparallel with said first servo valve means and providing secondcontrolled circuit for pressure fluid between said second source andsaid second fluid chamber, signal input means operating said first andsaid second valve means, said signal input means including meanssynchronizing operation of said first and said second servo valve meansto simultaneously direct pressurized fluid through each of saidcontrolled circuits.

8. The hydraulic actuator system defined in claim 7 wherein said firstand said second servo valve means each comprise a valve spool moveablymounted within a valve body, a plurality of ports in said valve bodyincluding first inlet and outlet ports connected to said first source,second inlet and outlet ports connected to said second source, a firstpair of distribution ports connected to said first fluid chamber, and asecond pair of distribution ports connected to said second fluidchamber, said valve spool being moveable within said valve body tosimultaneously control flow through said first inlet and outlet portsand said first distribution ports between said first source and saidfirst fluid chamber and through said second inlet and outlet ports andsaid second distribution ports between said second source and saidsecond fluid chamber.

9. The hydraulic actuator system as defined in claim 8 wherein saidvalve spools in said first and said second servo valves are slidablymounted within axial bores in said valve body to control the flow ofpressure fluid through said inlet and outlet ports and said distributionports.

10. The hydraulic actuator system defined in claim 9 wherein said valvespools are slidably mounted in coaxial relation in a single bore in acommon valve body.

11. The hydraulic actuator system defined in claim 9 wherein said inputmeans comprises linkage means independently connected to said valvespools in said first and said second servo valves for simultaneousmovement, said linkage means including means moving one of said valvespools independently of movement of the other valve spool in the eventof said other valve spool requiring excessive operating force.

12. The hydraulic actuator system defined in claim 11 wherein said meansindependently connecting said valve spools include prestressed resilientconnecting means.

1. A hydraulic actuator system comprising, in combination, first andsecond fluid chambers, a piston mounted in each of said fluid chambers,means connecting said pistons for equal, simultaneous movement withintheir respective fluid chambers, a first source of pressure fluid, firstconduit means connecting said first source to said first fluid chamber,a second source of pressure fluid, second conduit means connecting saidsecond source to said second fluid chamber, a servo valve assemblyoperatively connected in said first conduit means and providingcontrolled parallel fluid circuits between said first source and saidfirst fluid chamber, said servo valve assembly also being operativelyconnected in said second conduit means and providing controlled parallelfluid circuits between said second source and second fluid chamber, andsignal input means operating said servo valve assembly to control theflow of pressurized fluid through each of said fluid circuitssimultaneously.
 2. The hydraulic actuator system defined in claim 1wherein said servo valve assembly comprises first and second servovalves each operatively connected in said first conduit means and insaid second conduit means, said first and said second servo valvescooperating to provide said parallel circuits between said first sourceand said first fluid chamber and between said second source and saidsecond fluid chamber.
 3. The hydraulic actuator system defined in claim2 wherein said signal input means comprises an input assembly normallyapplying equal operating loads to said first and said second servovalves to thereby synchronize operation of the two valves.
 4. Thehydraulic actuator system defined in claim 3 wherein said signal inputmeans further comprises means for operating one of said servo valvesindependently of operation of the other of said servo valves in theevent said other servo valve becomes inoperable.
 5. The hydraulicactuator system as defined in claim 4 wherein said first and said secondservo valves are positioned in side-by-side relation, and said signalinput means comprises a whiffletree operatively connected to each ofsaid servo valves for operation thereof.
 6. The hydraulic actuatorsystem as defined in claim 4 wherein said signal input means furthercomprises a prestressed resilient connector assembly connected to eachof said servo valves, said connector assembly being deformable by eitherof said servo valves only upon said valves encountering a substantialincrease in resistance to operation.
 7. A hydraulic actuator systemcomprising, in combination, first and second fLuid chambers, a pair ofpistons mounted one in each of said fluid chambers, an output member,means connecting said pistons to said output member for simultaneousmovement therewith, a first source of pressure fluid, first conduitmeans connecting said first source to said first fluid chamber, a secondsource of pressure fluid, second conduit means connecting said secondsource to said second fluid chamber, first servo valve means connectedin said first conduit means and providing a controlled circuit forpressure fluid between said first source and said first fluid chamberand connected in said second conduit means and providing a controlledcircuit for pressure fluid between said second source and said secondfluid chamber, second servo valve means connected in said first conduitmeans in parallel with said first servo valve and providing a secondcontrolled circuit for pressure fluid between said first source and saidfirst fluid chamber and in said conduit means in parallel with saidfirst servo valve means and providing second controlled circuit forpressure fluid between said second source and said second fluid chamber,signal input means operating said first and said second valve means,said signal input means including means synchronizing operation of saidfirst and said second servo valve means to simultaneously directpressurized fluid through each of said controlled circuits.
 8. Thehydraulic actuator system defined in claim 7 wherein said first and saidsecond servo valve means each comprise a valve spool moveably mountedwithin a valve body, a plurality of ports in said valve body includingfirst inlet and outlet ports connected to said first source, secondinlet and outlet ports connected to said second source, a first pair ofdistribution ports connected to said first fluid chamber, and a secondpair of distribution ports connected to said second fluid chamber, saidvalve spool being moveable within said valve body to simultaneouslycontrol flow through said first inlet and outlet ports and said firstdistribution ports between said first source and said first fluidchamber and through said second inlet and outlet ports and said seconddistribution ports between said second source and said second fluidchamber.
 9. The hydraulic actuator system as defined in claim 8 whereinsaid valve spools in said first and said second servo valves areslidably mounted within axial bores in said valve body to control theflow of pressure fluid through said inlet and outlet ports and saiddistribution ports.
 10. The hydraulic actuator system defined in claim 9wherein said valve spools are slidably mounted in coaxial relation in asingle bore in a common valve body.
 11. The hydraulic actuator systemdefined in claim 9 wherein said input means comprises linkage meansindependently connected to said valve spools in said first and saidsecond servo valves for simultaneous movement, said linkage meansincluding means moving one of said valve spools independently ofmovement of the other valve spool in the event of said other valve spoolrequiring excessive operating force.
 12. The hydraulic actuator systemdefined in claim 11 wherein said means independently connecting saidvalve spools include prestressed resilient connecting means.